Naturally, the best thing to do was to try #Tapestry for myself. I added my Mastodon account and here's what I found:
1. Each post requires between 9 and 11 swipes to read with #VoiceOver. This can be reduced to 6 or 7 swipes per post in the collapsed timeline view, and 4 or 5 in the "mini" view. But the last of these doesn't include the text of posts.
2. Each post has three VoiceOver actions: the standard "Activate", "Open original", and "View details". "Activate" doesn't seem to do anything, "View details" opens a modal screen with similar info as on the timeline entry itself, and "Open original" opens the post on the Mastodon instance in a webview.
3. As you may've inferred from point number 2, you can't post, repost, reply, like, or bookmark from this app. You can mark a timeline entry, but that seems specific to the app and doesn't do anything on Mastodon.
4. There's a "Menu" button on each entry which has a few more buttons that aren't present as VoiceOver actions (e.g. "Translate" and "Share").

Right now, this is a no from me. The #accessibility is not good, and I can't really conceive an idea of reading my Mastodon timeline without interacting with any of the content in it.